It's important to view investing as a process, not a one-time event. Often, one of the reasons we don't start investing sooner is because, after paying bills and spending money elsewhere, we don't think there's anything left over.
By making a habit of investing regularly you gain two major advantages.
You help manage investment risk
When you invest regularly, you protect yourself against buying too much when prices are high and help reduce the temptation to sell at a bad time i.e., when prices are low.
You "Pay Yourself First"
A program of regular investment ensures that you attend to your long-term plan before you're tempted to spend your dollars on a short-term need. In addition, you can make sure you fully fund your IRA each year automatically.
These plans do not assure a profit and do not protect against loss in declining markets.